Physically Richardson IS better than Ingram, on the field not really. Ingram averaged 5.5 YPC over 3 years, Richardson 5.7. They're very similar, Richardson is faster but Ingram IMHO is a better natural runner he sees holes better, he cuts better, and he makes the first man miss more often. Richardson to me is more like McFadden he will have to adjust to not being able to run full speed into a hole on every carry. He runs very hard and will break tackles but he's not all that elusive. Ingram makes more guys miss and gets hit square less often. Ingram is the closest thing to Emmitt Smith I've seen, this year wasn't great for him but largely due to injury he wasn't really 100% most of the season.
Both will be great NFL RB's, I have a feeling assuming Ingram's foot is ok, that he will have the longer career because he doesn't get hit square as often.